Fix for division by zero in RecoBTag/PerformanceDB

[ferencek]

Added check that prevents division by zero

[StoyanStoynev]

@cmsbuild please run tests
the PR is super trivial but still...

[cmsbuild]

A new Pull Request was created by @ferencek (Dinko Ferencek) for CMSSW_7_2_X.

Fix for division by zero in RecoBTag/PerformanceDB

It involves the following packages:

RecoBTag/PerformanceDB

@cmsbuild, @nclopezo, @StoyanStoynev, @slava77 can you please review it and eventually sign? Thanks.
@ferencek, @acaudron, @pvmulder, @imarches this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@nclopezo you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[StoyanStoynev]

@cmsbuild please run tests

[davidlt]

@StoyanStoynev it's sitting in a queue waiting for a free machine to test

[cmsbuild]

+1
Tested at: 42ef699
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-5415/1010/summary.html

[cmsbuild]

+1
Tested at: 42ef699
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-5415/12/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-5415/12/summary.html

[StoyanStoynev]

+1
For 42ef699 .
Trivial bug fix (a "harmless" division by zero prompting warnings was fixed).
Jenkins fine, no diffs.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes (tests are also fine). @nclopezo can you please take care of it?